Leaflike shaft of a hip-joint prosthesis for anchoring in the femur

ABSTRACT

Leaflike shaft ( 1 ) of a hip-joint prosthesis for anchoring in the femur, according to a towards a distal end ( 5 ) [sic], with a femur-anchoring section ( 1   a   , . . . 1   i ) having a long axis (A) and with a prosthesis neck ( 2 ), wherein the femur-anchoring section  1   a   , . . . 1   i ) has a substantially rectangular external contour in a plane perpendicular to the long axis (A), optionally with recesses in the side edges and/or at the corners.

DESCRIPTION

[0001] The invention relates to a leaflike shaft of a hip-joint prosthesis for anchoring in the femur, with a femur-anchoring section and a prosthesis neck.

[0002] Profiled shafts of this kind are generally known. As only a few examples in this regard reference is made to the patents EP 0 427 902 B1 or EP 0 244 610 B1 or U.S. Pat. No. 4,908,035.

[0003] As a rule the anchoring section of a shaft of the kind in question here is constructed with smooth surfaces. In EP 0 427 902 B1 it is proposed to construct one section of the shaft with contact surfaces provided with sawteeth. This measure is intended to improve fusion of the shaft to the bony substance.

[0004] It is disclosed in the patent CH-A 642 252 that the anterior and posterior leaf surfaces of the leaf part of a shaft are provided with groove-like indentations. However, bone tissue grows poorly into these. The tissue that fills up these indentations is generally a connective tissue with only slight stability.

[0005] The object of the present invention is to configure the femur-anchoring section of a leaflike shaft in such a way that the the tissue growing onto the prosthesis consists to the greatest possible extent of spongy bone tissue, so as to ensure long-term, firm retention of the shaft in the femur.

[0006] This object is achieved by a leaflike shaft with the characteristics given in claim 1.

[0007] The invention includes the fundamental idea that the femur-anchoring section of the shaft is substantially rectangular in cross section, so that in simplified (ignoring the tapering toward the tip) terms it is constructed as a “four-edged” profile, in particular as

[0008] oblique-cross profile

[0009] H profile

[0010] double-H or -comb profile

[0011] rectangular hollow profile

[0012] rectangular facet profile

[0013] rectangular notch profile

[0014] approximately trapezoidal profile (with or without recesses at the sides or in the interior)

[0015] or the like.

[0016] These profiles all exhibit, to a greater or lesser extent, the property that in the space between the anchoring section of the shaft and the wall of the surgically created cavity spongy bone tissue forms, so that revascularization of the bone occurs. The alternatives in accordance with the invention have the advantage that their periphery comprises substantially four edges, situated at the corners of a rectangle or trapezoid that extends perpendicular to the central axis of the shaft. This basic shape of a shaft has been found in practice to be particularly advantageous for the revascularization of the bone tissue.

[0017] It has further been found that a predetermined overdimensioning of the side surfaces of the shaft in comparison to the “rasped” dimension (“null dimension”)—with the exception of the edge regions, which should fit precisely—is advantageous in this respect, especially in the proximal section of the shaft.

[0018] With the further development in accordance with the invention the revascularization of the bone tissue is additionally promoted, while on one hand the necessary stability or solidity of the shaft is preserved, but on the other hand the intervening space between shaft and operation-cavity wall is enlarged, with the result that a greater amount of new spongiosa is formed.

[0019] Advantageous details of the prosthesis shaft in accordance with the invention are presented in the subordinate claims and explained in detail in the following description of exemplary embodiments with reference to the attached drawings, wherein

[0020]FIG. 1 is a perspective view of a leaflike shaft, the femur-anchoring section of which is further developed in accordance with the invention;

[0021] FIGS. 2-9 show various cross sections of the anchoring section of the shaft according to FIG. 1 along the line A-A in FIG. 1, and

[0022]FIG. 10 shows another preferred embodiment in cross section.

[0023]FIG. 1 shows, in perspective, a leaflike shaft 1 of a hip-joint prosthesis for anchoring in the femur. The exemplary embodiment shown here comprises an anchoring section 1 a, . . . 1 i (see FIGS. 2 to 10), which expands conically on all sides from a distal end 5 to the proximal region, where on the medial side it merges with a continuously curving arch 8. This arch 8 is continuous with a prosthesis neck 2, onto which is set a conically tapering peg 3 which receives a spherical joint head. The prosthesis neck axis intersects the central long axis (not shown in FIG. 1) of the shaft and the anchoring section 1 a . . . 1 i at an angle that corresponds substantially to the angle between the neck and axis of the femur in a natural hip joint.

[0024] Laterally in the proximal region of the shaft 1 a trochanter wing 4 is formed, which is laterally delimited by a side surface 9. The transition between the lateral surface and the posterior or anterior surface is defined by a slanted edge 6 that extends from distal to proximal in the region of the trochanter wing 4. The “leaf” of the shaft 1 is defined in the proximal region and is identified by the reference numeral 7.

[0025] In FIGS. 2-10 various cross sections or profile shapes of anchoring sections 1 a . . . 1 i of the shaft 1 are shown.

[0026] According to FIG. 2, the anchoring section 1 a is constructed as an oblique-cross profile, the limbs of which form V-shaped grooves 11 a, 11 b on the anterior and posterior aspects respectively, each of which has an angle greater than 90°, and laterally and medially form V-shaped grooves 12 a, 12 b with an angle smaller than 90°.

[0027] In the embodiment according to FIG. 3 the anchoring section 1 b of the shaft 1 is constructed as an H profile. This profile comprises rectangular recesses 13 a, 13 b on the posterior and the anterior aspect.

[0028]FIG. 4 shows another variant, in which the anchoring section 1 c of the shaft 1 is a double-H profile or double-comb profile, in that rectangular longitudinal grooves 14 a, 14 b, 14 c, 14 d are formed on the posterior and anterior aspects of the anchoring section.

[0029] In the variant shown in FIG. 5, the anchoring section 1 d of the shaft 1 is roughly rectangular in cross section, with concave facets formed at the four corners.

[0030] The embodiments according to FIGS. 6 and 7 comprise an anchoring section 1 e and 1 f, respectively, in the form of a rectangular hollow profile, the embodiment according to FIG. 6 having a cavity 15 that is rectangular in cross section, whereas in the embodiment according to FIG. 7 the cross section of the cavity 16 is elliptical. These two variants are characterized by an especially high stability of the anchoring section, accompanied by low weight.

[0031] The variant according to FIG. 8 has an anchoring section 1 g defined by a rectangular notched profile. On the anterior and on the posterior aspect there are formed two spaced-apart longitudinal notches 17 a, 17 b and 17 c, 17 d respectively. Each of these four notches is V-shaped. On the lateral and on the medial aspect one longitudinal notch 18 a, 18 b is provided, which likewise are V-shaped notches or longitudinal grooves. The corners that delimit the outline of the anchoring section 1 g, like those in the embodiment according to FIGS. 6 and 7, can comprise flattened or concave facets like those shown in FIG. 5.

[0032] In the embodiment according to FIG. 6 the rectangular cavity 15 can be subdivided by a web or a cross-strut extending in the long direction of the shaft.

[0033] The embodiment according to FIG. 8, like that in FIG. 5, can be constructed as a hollow profile with a cavity that extends in the long direction of the shaft and has a circular or oval or elliptical cross section.

[0034] The embodiment of an anchoring section lh shown in FIG. 9 differs from the embodiments in FIGS. 2-8 in having a trapezoidal cross section, which in this case is symmetrical with two equally long longer sides a in cross section, which correspond to the anterior and posterior surfaces, and two differently long shorter sides b, c, of which the shorter one is medial and the longer one lateral. This symmetrical trapezoidal shape is at present regarded as preferred, but in principle prosthesis shafts with asymmetrical trapezoidal cross sections can also be constructed.

[0035] The cross-sectional shapes shown in FIGS. 2-8 (which in those figures are, so to speak, inscribed within a rectangle) can also be modified to give them a basically trapezoidal shape: for instance, an asymmetrical oblique cross, an “H” with a longer and a shorter limb, an embodiment similar to that in FIG. 4 with three differently long limbs, an embodiment corresponding to FIG. 5 but with concave facets in the corner regions of a trapezoidal cross section, or various hollow profiles with a trapezoidal external configuration.

[0036] In FIG. 10, to illustrate an additional special embodiment of the anchoring section of the shaft prosthesis in accordance with the invention, a cross-sectional shape is shown which again is basically rectangular and at all corners exhibits stepwise chamfered regions 19. The outer contour indicated by the dashed line approximately represents a conventional shaft cross section for the same application, with chamfered regions at an angle of 45° to the side surfaces. It is evident that the proposed new design (indicated by a continuous line) is overdimensioned in comparison with this known embodiment over the greater part of all the side surfaces. However, all the chamfered regions have a middle section, the level of which coincides with the level of chamfering of the corresponding conventional prosthesis shaft. On either side of and parallel to this section are chamfered steps, set back slightly from the middle section.

[0037] This embodiment is based on the idea that it is advantageous for a prosthesis shaft—at least in its proximal region—to be overdimensioned by a predetermined amount in comparison to the dimensions of the prepared cavity in the femur (i.e., in comparison to the “rasped dimension”), inasmuch as this overdimensioning increases the pressure of the surfaces against the surrounding bone tissue and thus causes a degree of bone compression. When the ordinary forging precision is also taken into account, the overdimensioning amounts to about 1-3% of the “rasped dimension” in the marrow space, which is also to be understood as the “null dimension”.

[0038] In the corner regions, by contrast, the fit should be as precise as possible so as not to place the corticalis under excessive stress. Therefore the corner regions are reduced to the exact rasped dimension just prior to implantation. A final shaping to produce the stepped corner configuration shown in FIG. 10 has proved to be relatively easy to accomplish and advantageously effective; in principle, however, other fine structures in the corner region are possible, with which the dimensional conformity of the corners (more precisely: the chamfers) can be made consistent with an overdimensioning of the remaining side and end surfaces—for example, rounding or additional chamfered regions at an angle to the main chamfer.

[0039] All the characteristics disclosed in the application documents are claimed as essential to the invention insofar as they are new to the state of the art individually or in combination.

LIST OF REFERENCE NUMERALS

[0040]1 Shaft

[0041]1 a, 1 b, 1 c, 1 d, 1 e,

[0042]1 f, 1 g, 1 h, 1 i Femur-anchoring section

[0043]2 Prosthesis neck

[0044]3 Peg in form of truncated cone

[0045]4 Trochanter wing

[0046]5 Distal end

[0047]6 Facet

[0048]7 Section of the shaft

[0049]8 Arch

[0050]9 Lateral boundary surface

[0051]11 a, 11 b V-groove

[0052]12 a, 12 b V-groove

[0053]13 a, 13 b Rectangular groove

[0054]14 a, 14 b, 14 c, 14 d Rectangular groove

[0055]15 Rectangular groove

[0056]16 Oval cavity

[0057]17 a, 17 b, 17 c, 17 d, 18 a, 18 b Longitudinal notch

[0058]19 Stepped chamfer

[0059] a Long side

[0060] b,c End face 

1. Leaflike shaft (1) of a hip-joint prosthesis for anchoring in the femur, with a femur-anchoring section (1 a, . . . 1 i) that tapers toward a distal end (5) and has a long axis (A) and a prosthesis neck (2), characterized in that the femur-anchoring section (1 a, 1 i) has an external contour in a plane perpendicular to the long axis (A) that is substantially rectangular, optionally with recesses in the sides and/or at the corners and/or in the interior.
 2. Shaft according to claim 1, characterized in that the anchoring section (1 a) is constructed in the plane perpendicular to the long axis (A) as an oblique cross, such that four limbs of a cross (FIG. 2) form on the anterior and on the posterior aspect a V-shaped groove (11 a, 11 b) having an opening angle of more than 90° and on the lateral and the medial aspect a V-shaped groove (12 a, 12 b) with an opening angle of less than 90°.
 3. Shaft according to claim 1, characterized in that the anchoring sections (1 d-1 g; 1 i) in a plane perpendicular to the long axis (A) have substantially the shape of a rectangle, with cut-outs in the region of at.least one side edge and/or the corners and/or in the interior.
 4. Shaft according to claim 1, characterized in that the anchoring section (1 h) in a plane perpendicular to the long axis (A) has substantially the shape of a trapezoid, in particular with cut-outs in the region of at least one side edge and/or the corners and/or in the interior.
 5. Shaft according to claim 4, characterized in that the shape of the trapezoid is substantially symmetrical, such that the anterior and posterior side edges of the trapezoid are of equal length and are longer than the lateral and medial side edges, of which the medial side edge is the shorter.
 6. Shaft according to one of the claims 1 or 3-5, characterized in that a cavity (15; 16) defined by a removal of material in the interior of the anchoring section (le; if) is substantially matched in shape to the external contour of the anchoring section, being made rectangular or trapezoidal or circular or elliptical.
 7. Shaft according to one of the claims 3-5, characterized in that in each of the side edges that correspond to the posterior and to the anterior surface two or more substantially V-, U- or C-shaped recesses (17 a-17 d) are formed and in particular also in each of the edges that correspond to the lateral and/or medial surface at least one V-, U- or C-shaped recess (18 a, 18 b) is formed.
 8. Shaft according to claim 1 or one of the claims 3-7, characterized in that at least in one of the longitudinal edge regions of the anchoring section (1 i), preferably in the regions of all its long edges, a chamfer (19) is provided with a stepped, additionally angled or rounded configuration, and the remaining side-surface regions in at least a proximal subsection of the longitudinal extent of the anchoring section are overdimensioned with respect to a “rasping dimension” used for preparation of the femur.
 9. Shaft according to claim 8, characterized in that the overdimensioning amounts to between 1 and 3%, such that the anchoring section is forged in the overdimensioned range and the chamfered region or regions is/are subsequently machined to smaller dimensions. 